Abstract: :
Purpose: The rabbit eye was used for safety testing of a 103Pdhigh dose rate device being developed by Theragenics Corporation(Buford, GA) for potential use in treatment of Age-Related MacularDegeneration (ARMD).Methods: In this pilot study, conductedat the Charles River Laboratories (Worcester, MA), the righteye of four groups of male New Zealand White rabbits were irradiatedwith a 0, 10, 20, or 50 Gy dose in a single 5 to 25 minute fraction.A 5 mm aperture 103Pd applicator was positioned adjacent tothe optic nerve and held in place to deliver the prescribeddose to a depth of 3 mm into the eye. The left eye of each rabbitwas used as a control. During the study, daily clinical observations,weekly ophthalmic observations and body weights were recorded.An electroretinogram and a final ophthalmic examination wereperformed on each rabbit at the end of the 29 day study. OnDay 29, all rabbits were euthanized, and both eyes were enucleatedand submitted for histopathologic examination. The eyes werefixed in Davidson's fixative. A central calotte that includedthe treatment site from each eye was processed, embedded inparaffin, and sectioned. The glass slides were stained withhematoxylin and eosin, and then evaluated by light microscopy.Results: On day 5, the rabbit eyes in all treatment groupsregardless of delivered radiation dose had mild conjunctivalinjection attributed to the treatment procedure. Electroretinogramswere comparable for both eyes (treated and untreated) of allbut two rabbits. In both of these rabbits, the low A-B amplitudewas thought to have been a preexisting condition. Final ophthalmicfindings for two rabbit eyes in the high-dose group (50 Gy)revealed chorioretinal hypovascularization that appeared tobe treatment related. Two retinal detachments were noted inuntreated eyes during the final ophthalmic examination. Histopathologicexamination of the additional rabbit eye in the high dose groupshowed focal retinal atrophy involving the outer nuclear andphotoreceptor layers of the retina in the posterior portionof the globe. No lenticular or scleral side effects were noted.Conclusion: The rabbit eye was used as an ocular model forsafety testing of the 103Pd high dose rate applicator. No adverseevents could be attributed to the treatment methodology or thephysical parameters of the device. An acute vascular effectwithin the choroid and retina appeared at a treatment dose of50 Gy.